1. Field of the Invention
This invention relates, in general, to an interface between melt channels of two interfacing components. In this context, the invention relates particularly, but not exclusively, to melt channel alignment between a nozzle and a distribution component in a molding system and more especially to a dual interface that provides a centrally located fluid egress point that is located between and commonly feeds two independently functioning fluid distribution systems.
2. Summary of the Prior Art
In prior art systems where, for example, a nozzle interface to a sprue bushing that feeds into a single hot runner or the like, melt channel alignment from the distributor into the sprue bushing can be maintained through use of a mechanical adjustment of the carriage assembly. As will be appreciated, the carriage assembly supports the injection unit/screw. Of course, this assumes that any central misalignment between the respective melt channels in a distributor (e.g. the nozzle of the screw) and the mold sprue bushing (or the like) is itself within the specified correctable (adjustment) range for the carriage assembly. Unfortunately, however, in multi-mold systems where a single distributor simultaneously feeds at least two remotely (but complementarily) located mold sprue bushings, use of the carriage assembly adjustment may act to correct alignment in one of the melt channel paths of the system, but may simultaneously exacerbate melt leakage in the other melt channel by increasing misalignment. In other words, channel misalignment arises from a relative lateral shift in respective centre lines for the different melt channels.
The undesirably mechanism by which melt leaks at the interface of, for example, the nozzle is sometimes referred to as “drooling”.
In an exemplary instance of an injection molding system, failure to provide an acceptable horizontal radial alignment and, consequently, an effective seal between the nozzle and the runner systems can compromise system operation. Melt leakage can, for example, cause: i) parts to be mis-formed, e.g. through short shot delivery issues; and ii) unacceptably early mold component wear arising. In any event, there is a related financial expense to the mold operator. Indeed, radial misalignment can never be avoided because of thermal elongation problems, especially in relation to a runner (such as a hot runner) system that has a typically operational temperature of about three hundred degrees Celsius.
It is established practice that the interface between a nozzle and the sprue has been realised a radial interface in which a smaller nozzle (convex) radius fits into a larger (concave) radius or seat in the sprue. By accomplishing radial alignment, a contiguous melt channel is realised between the nozzle and the sprue through the surrounding annular contact surface. Moreover, some form of return spring provides physical loading of the interface between the external contact surfaces of the nozzle and the sprue, thereby improving the resultant seal.
Even a small misalignment results in limited point contact around only a portion of the circumference of the seat. Consequently, when there is a radial misalignment in the central axis of the melt channels (of the nozzle and sprue bushing) a crack to the melt channel appears.
In the context of a nozzle that feeds a plurality of distributors (such as when a melt delivery system is located within a centre-section carrier of a stack mold), it is usual that this arrangement is much stiffer in a radial direction than a standard single injection nozzle configuration. The additional stiffness arises because, overall, the entire melt delivery system (and particularly the nozzle) is considerably shorter in size. Unfortunately, there is an associated increase in precision alignment required in mounting such systems and hence a higher likelihood that drooling can occur from ineffectual (i.e. partial) sealing at the nozzle-sprue interface.
U.S. Pat. No. 4,299,791 describes a method of avoiding drool by varying the volume of the sprue (of the mold) by movement of a plunger in radially-shaped nozzle. U.S. Pat. No. 4,917,595 also shows a spherically shaped nozzle that locates within a correspondingly shaped nozzle touch sprue bushing, whereby melt channel alignment between the nozzle and sprue is achieved through this “ball and socket”-type alignment.